Why is temperature sensitivity important for the success of common respiratory viruses?

Abstract

This review explores the idea that temperature sensitivity is an important factor in determining the success of respiratory viruses as human parasites. The review discusses several questions. What is viral temperature sensitivity? At what range of temperatures are common respiratory viruses sensitive? What is the mechanism for their temperature sensitivity? What is the range of temperature along the human airway? What is it that makes respiratory viruses such successful parasites of the human airway? What is the role of temperature sensitivity in respiratory zoonoses? A definition of temperature sensitivity is proposed, as "the property of a virus to replicate poorly or not at all, at the normal body temperature of the host (restrictive temperature), but to replicate well at the lower temperatures found in the upper airway of the host (permissive temperature)." Temperature sensitivity may influence the success of a respiratory virus in several ways. Firstly; by restricting the infection to the upper airways and reducing the chance of systemic infection that may reduce host mobility and increase mortality, and thus limit the spread of the virus. Secondly; by causing a mild upper airway illness with a limited immune response compared to systemic infection, which means that persistent herd immunity does not develop to the same extent as with systemic infections, and re-infection may occur later. Thirdly; infection of the upper airway triggers local reflex rhinorrhea, coughing and sneezing which aid the exit of the virus from the host and the spread of infection in the community.

FIGURE 1

Airway temperatures. Nasal temperatures are nasal mucosal temperatures measured during inspiration of ambient air at 25C (Lindemann et al 2002). Tracheal temperature is for inspiratory air temperature (Cole 1988) See text for details

FIGURE 2

Diagram to illustrate transmission of respiratory viruses. The Infected host is illustrated on the left in red and the susceptible host on the right in blue. Infectious nasal fluid can reach the susceptible host by aerosols generated by coughs, or via fomites and hand transmission the nose and eye